BEIRUT – A Hezbollah commander and several fighters have been killed inside Syria, a Lebanese security official said Tuesday, a development that could stoke already soaring tensions over the Lebanese militant group’s role in the civil war next door.

Hezbollah’s reputation has taken a beating over its support for the Syrian regime, but any sign that the group’s fighters are taking part in the battle raises fears that the conflict could expand into a wider fight engulfing the region.

Hezbollah has stood by Syrian President Bashar Assad since the uprising began 18 months ago, even though the group supported revolts in Egypt, Tunisia, Libya and Bahrain.

Assad’s fall would be a dire scenario for Hezbollah. Any new regime led by Syria’s majority Sunni Muslims would likely be far less friendly – or even outright hostile – to Shiite Muslim Hezbollah. Iran remains the group’s most important patron, but Syria is a crucial supply route. Without it, Hezbollah will struggle to get money and weapons as easily.

It was not immediately clear how the Hezbollah militants were killed or whether they had been fighting alongside the Syrian army. But Hezbollah’s newspaper al-Intiqad said Hezbollah commander Ali Hussein Nassif, who is also known as Abu Abbas, was killed “while performing his jihadi duties.” It did not say when or where he was killed.

A Lebanese security official said Nassif was killed in Syria and his body was returned to Lebanon through the Masnaa border crossing on Sunday. Speaking on condition of anonymity, the official said the bodies of several other Hezbollah fighters have been brought back to Lebanon in recent days.